Fin field effect transistors having capping insulation layers

ABSTRACT

A field effect transistor includes a vertical fin-shaped semiconductor active region having an upper surface and a pair of opposing sidewalls on a substrate, and an insulated gate electrode on the upper surface and opposing sidewalls of the fin-shaped active region. The insulated gate electrode includes a capping gate insulation layer having a thickness sufficient to preclude formation of an inversion-layer channel along the upper surface of the fin-shaped active region when the transistor is disposed in a forward on-state mode of operation. Related fabrication methods are also discussed.

CLAIM OF PRIORITY

This application claims priority to and is a divisional of parent application Ser. No. 10/936,033, filed Sep. 8, 2004, the disclosure of which is hereby incorporated herein by reference, which claims the benefit of Korean Application No. 10-2003-76960, filed on Oct. 31, 2003 the disclosure of which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to semiconductor devices, and more specifically, to field effect transistors and methods of forming the same.

BACKGROUND OF THE INVENTION

As semiconductor devices become highly integrated, transistor size may be reduced, which may result in a variety of operational and structural problems. For instance, short channel effects may be increased, and punch-through characteristics between source and drain regions may deteriorate. In addition, the turn-on current of the transistor may be decreased, and transistor performance may be degraded.

To address some of these problems, fin field effect transistors (Fin-FETs) have been developed. A fin field effect transistor can include a gate electrode on an upper surface and sidewalls of a silicon fin that vertically protrudes from a semiconductor substrate. Source and drain regions may also be formed in the silicon fin on opposite sides of the gate electrode. Thus, a channel region may be formed at both sidewalls and at the upper surface of the silicon fin, such that the channel width of the transistor may be increased. In addition, the gate electrode can control the channel region at both sides, thereby improving device controllability. Furthermore, turn-on current may be increased due to the greater channel width, thereby improving both performance as well as punch-through characteristics between the source and drain.

However, problems may occur at corner portions of the channel region, i.e. where a sidewall portion and a top surface portion of the channel region meet.

FIG. 1 is a perspective view illustrating a conventional fin field effect transistor (Fin FET). FIG. 2 is a cross-sectional view of the Fin FET taken along line I-I′ of FIG. 1.

Referring to FIGS. 1 and 2, a silicon fin 2 vertically protrudes from a semiconductor substrate 1. A gate electrode 5 crosses over the silicon fin 2. In other words, the gate electrode 5 passes over both sidewalls and the upper surface of the silicon fin 2. A gate oxide layer 3 is formed between the gate electrode 5 and the silicon fin 2. Source/drain regions 6 are formed in the silicon fin 2 on both sides of the gate electrode 5.

The gate electrode 5 may include three parts: a first gate 4 a at one sidewall of the silicon fin 2, a second gate 4 b at the upper surface of the silicon fin 2, and a third gate 4 c at another sidewall of the silicon fin 2. Accordingly, the channel region may include vertical channel portions formed at both sidewalls of the silicon fin 2 and a top channel portion formed at the upper surface of the silicon fin 2.

However, when a voltage is applied to the gate electrode 5 of a fin field effect transistor having the above-mentioned structure, the electric field may be concentrated on corner portions “A” of the fin 2, i.e. where the vertical channel portions meet the top channel portions. This may result in a “hump” in the subthreshold current. In other words, leakage current may occur at voltages lower than threshold voltage of the fin field effect transistor. As a result, characteristics of the fin field effect transistor may be degraded.

SUMMARY OF THE INVENTION

According to some embodiments of the present invention, a field effect transistor may include a vertical fin-shaped semiconductor active region having an upper surface and a pair of opposing sidewalls on a substrate, and an insulated gate electrode on the upper surface and opposing sidewalls of the fin-shaped active region. The insulated gate electrode may include a capping gate insulation layer having a thickness sufficient to preclude formation of an inversion-layer channel along the upper surface of the fin-shaped active region when the transistor is disposed in a forward on-state mode of operation.

In other embodiments, the insulated gate electrode may further include a sidewall gate insulation layer on upper sidewalls of the fin-shaped active region. The thickness of the capping gate insulation layer may be greater than a thickness of the sidewall gate insulation layer. In further embodiments, the capping gate insulation layer and the sidewall gate insulation layer may be formed of oxide layers.

In some embodiments, the insulated gate electrode may further include a sidewall gate insulation layer on upper sidewalls of the fin-shaped active region having a thickness similar to the thickness of the capping gate insulation layer. The capping gate insulation layer may be formed of a material having a higher dielectric strength than the sidewall gate insulation layer.

In other embodiments, the field effect transistor may further include a buffer oxide layer on lower sidewalls of the fin-shaped active region, a liner layer on the buffer oxide layer and extending on sidewalls of the fin-shaped active region away from the substrate, and an insulation layer on the liner layer and separated from the fin-shaped active region by the liner layer. The transistor may also include a supplemental insulation layer on the substrate adjacent lower sidewalls of the fin-shaped active region.

In some embodiments, the field effect transistor may also include a planar active region adjacent the fin-shaped active region on the substrate.

According to other embodiments of the present invention, a method of forming a vertical channel field effect transistor on a fin-shaped active region of a semiconductor substrate may include forming an insulated gate electrode on an upper surface and opposing sidewalls of the fin-shaped active region. The step of forming the insulated gate electrode may include forming a capping gate insulation layer on the upper surface of the fin-shaped active region to a thickness sufficient to preclude formation of an inversion-layer channel along the upper surface when the transistor is disposed in a forward on-state mode of operation.

In some embodiments, the step of forming the insulated gate electrode may further include forming a sidewall gate insulation layer on sidewalls of the fin-shaped active region. The capping gate insulation layer may be formed to a thickness greater than a thickness of the sidewall gate insulation layer. In further embodiments, the step of forming the capping gate insulation layer may include thermally oxidizing the upper surface of the fin-shaped active region.

In other embodiments, the step of forming the insulated gate electrode may further include forming a sidewall gate insulation layer on sidewalls of the fin-shaped active region having a thickness similar to the thickness of the capping gate insulation layer. The capping gate insulation layer may be formed of a material having a higher dielectric strength than the sidewall gate insulation layer.

In some embodiments, forming a sidewall gate insulation layer may include forming a buffer oxide layer on the substrate, forming a liner layer on the buffer oxide layer, forming a insulation layer on the liner layer, and planarizing the insulation layer, the liner layer, and the buffer oxide layer to expose the upper surface of the fin-shaped active region. The method may further include recessing the liner layer to expose a portion the buffer oxide layer on upper sidewalls of the fin-shaped active region, removing the exposed portion of the buffer oxide layer to expose the upper sidewalls of the fin-shaped active region, and then forming a sidewall gate insulation layer on the exposed upper sidewalls of the fin-shaped active region. In addition, a supplemental insulation layer may be formed on the buffer oxide layer prior to forming the liner layer.

In other embodiments, the substrate may include a planar active region adjacent the fin-shaped active region. After the step of planarizing, the method may further include forming an oxidation barrier layer on the fin active region and the planar active region, and patterning the oxidation barrier layer to expose the top surface of the fin active region. The step of recessing the liner layer may include simultaneously recessing the liner layer on the fin-shaped active region and the oxidation barrier layer on the planar active region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating a conventional fin field effect transistor.

FIG. 2 is a cross-sectional view of a conventional fin field effect transistor, taken along line I-I′ of FIG. 1.

FIG. 3 is a perspective view of a semiconductor device according to various embodiments of the present invention.

FIGS. 4 to 10 are cross-sectional views illustrating methods of forming a semiconductor device according to various embodiments of the present invention taken along lines II-II′ and III-III′ of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the thickness of layers and regions are exaggerated for clarity. It will be understood that when an element such as a layer, region or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. It will be understood that when an element such as a layer, region or substrate is referred to as “under” another element, it can be directly under the other element or intervening elements may also be present. It will also be understood that the term “and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

Furthermore, relative terms such as beneath may be used herein to describe one layer or region's relationship to another layer or region as illustrated in the Figures. It will be understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. For example, if the device in the Figures is turned over, layers or regions described as “beneath” other layers or regions would now be oriented “above” these other layers or regions. The term “beneath” is intended to encompass both above and beneath in this situation. Like numbers refer to like elements throughout.

The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms “a”, “an ” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Embodiments of the invention are described herein with reference to cross-section illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of the invention. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the invention should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and/or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the invention.

Unless otherwise defined, all terms used in disclosing embodiments of the invention, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, and are not necessarily limited to the specific definitions known at the time of the present invention being described. Accordingly, these terms can include equivalent terms that are created after such time. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety.

FIG. 3 is a perspective view of a semiconductor device according to various embodiments of the present invention.

Referring to FIG. 3, a substrate 100 includes a first region a and a second region b. A fin field effect transistor is formed in the first region a. Cell arrays of semiconductor memory devices may also be formed in the first region a. A flat or planar-type field effect transistor is formed in the second region b. The second region b may be a peripheral circuit region in semiconductor memory devices.

A fin-shaped semiconductor active region 105 a is formed in the substrate 100 of the first region a. This fin-shaped active region 105 a vertically protrudes from the substrate 100. A planar active region 105 b is formed on the substrate 100 of the second region b. The planar active region 105 b also vertically protrudes from the substrate 100. The area of the top surface of the planar active region 105 b is greater than that of the fin active region 105 a.

A first liner 111 a′ and a first device isolation layer 113 a are sequentially stacked along a sidewall of the fin active region 105 a. The first liner 111 a′ is positioned on a lower portion of the sidewall of the fin active region 105 a, thereby exposing an upper portion of the sidewall of the fin active region 105 a. The top surface of the first liner 111 a′ is lower than the top surface of the first device isolation layer 113 a, such that a groove is defined by the exposed upper sidewall of the fin active region 105 a, the top surface of the first liner 111 a′, and the upper sidewall of the first device isolation layer 113 a. A portion of the first liner 111 a′ also extends along a surface of the substrate 100 neighboring the fin active region 105 a and is in contact with a bottom surface of the first device isolation layer 113 a. As such, the first liner 111 a′ is positioned between the first device isolation layer 113 a and the substrate 100.

A second liner 111 b and a second device isolation layer 113 b are sequentially stacked along a sidewall of the planar active region 105 b. The second liner 111 b may cover a majority of the sidewall of the planar active region 105 b. A portion of the second liner 111 b also extends along a surface of the substrate 100 neighboring the planar active region 105 b and is in contact with a bottom surface of the second device isolation layer 113 b. As such, the second liner 111 b is positioned between the second device isolation layer 113 b and the substrate 100.

The first and second device isolation layers 113 a and 113 b may be made of silicon oxide. Preferably, the first and second liners 111 a′ and 111 b may be made of an insulation layer having an etch selectivity with respect to the first and second device isolation layer 113 a and 113 b. For example, the first and second liners 111 a′ and 111 b may be made of silicon nitride.

A buffer oxide layer 107 is positioned between the first liner 111 a′ and the fin active region 105 a, and between the second liner 111 b and the planar active region 105 b. Portions of the first and second liners 111 a′ and 111 b may be positioned on the buffer oxide layer 107. The buffer oxide layer 107 may be formed of a thermal oxide or a chemical vapor deposition (CVD) oxide.

A supplemental insulation layer 109 may be positioned between the first liner 111 a′ and the substrate 100, and between the second liner 111 b and the substrate 100. The supplemental insulation layer 109 may also be positioned on the buffer oxide layer 107, and may be in contact with portions of buffer oxide layer 107 on the lower sidewall of the fin and planar active regions 105 a and 105 b. The supplemental insulation layer 109 may be made of a Spin-On-Glass (SOG) layer such as HSQ (Hydrogen Silses Quioxane), or of a polysilazane material.

Still referring to FIG. 3, a capping gate insulation layer 120 is formed on the upper surface of the fin active region 105 a. The capping insulation layer 120 may preferably be made of a thermal oxide. A first gate insulation layer 122 a is formed on at least the exposed upper sidewall of the fin active region 105 a, and a second gate insulation layer 122 b is formed on the upper surface of the planar active region 105 b. The thickness of the capping insulation layer 120 may be greater than that of the first and second gate insulation layers 122 a and 122 b. The first and second gate insulation layers 122 a and 122 b may preferably be formed to a thickness suitable for a fin field effect transistor and a planar field effect transistor, respectively. Also, the first and second gate insulation layers 122 a and 122 b may preferably be made of the same material. For example, the first and second gate insulation layers 122 a and 122 b may both be made of a thermal oxide or a CVD oxide.

A first gate electrode 125 is formed on the fin active region 105 a, on the capping insulation layer 120, and in the groove defined by the exposed upper sidewall of the fin active region 105 a, the top surface of the first liner 111 a′, and the upper sidewall of the first device isolation layer 113 a. In other words, the first gate electrode 125 is formed over the upper surface and both upper sidewalls of the fin active region 105 a. As such, the capping insulation layer 120 is positioned between the first gate electrode 125 and the upper surface of the fin active region 105 a, and the first gate insulation layer 122 a is positioned between the first gate electrode 125 and the upper sidewalls of the fin active region 105 a. A second gate electrode 127 is formed on the upper surface of the planar active region 105 b. The second gate insulation layer 122 b is positioned between the second gate electrode 127 and the upper surface of the planar active region 105 b.

The first and second gate electrodes 125 and 127 may be made of doped polysilicon, polycide or other conductive materials. Other such conductive materials may include metals (such as tungsten or molybdenum), conductive metal nitrides (such as titanium nitride, tantalum nitride or tungsten nitride) or metal silicides (such as tungsten silicide or titanium silicide).

First source/drain regions 128 a are formed in the fin active region 105 a at both sides of the first gate electrode 125, and second source/drain regions 128 b are formed in the planar active region 105 b at both sides of the second gate electrode 127. The first and second source/drain regions 128 a and 128 b may be formed by doping the fin and planar active regions 105 a and 105 b with impurities of the same type. In addition, the first and second source/drain regions 128 a and 128 b may also be doped with the same impurity concentration. Alternatively, the first and second source/drain regions 128 a and 128 b may be doped with different impurity types and in different concentrations. Current may flow between respective source and drain regions when the semiconductor device is biased in a forward on-state mode of operation, i.e. when the gate voltage is greater than the threshold voltage.

In the semiconductor device described above, the thickness of the capping gate insulation layer 120 is sufficiently greater than that of the first gate insulation layer 122 a, such that an inversion-layer channel is not formed at the upper surface of the fin active region 105 a of the fin field effect transistor in the first region a when the transistor is disposed in a forward on-state mode of operation. Alternatively, the thickness of the capping gate insulation layer 120 may be similar to that of the first gate insulation layer 122 a. In this case, the capping gate insulation layer 120 may be formed of a material with a higher dielectric strength than that of the first gate insulation layer 122 a, such that a greater gate bias may be required to form an inversion-layer channel at the upper surface of the fin active region 105 a. In either case, responsive to a sufficient gate bias, inversion-layer channels are formed adjacent only the upper sidewalls of the fin active region 150 a. Thus, the channel region of the fin field effect transistor includes only the vertical channels adjacent both upper sidewalls of the fin active region 105 a. As a result, the “hump” phenomenon may be reduced, thereby improving the characteristics of the fin field effect transistor.

In addition, the second liner 111 b is formed on the entire sidewall of the planar active region 105 b, such that a groove may not be formed around the planar active region 105 b. Also, the second gate insulation layer 122 b is positioned between the second gate electrode 127 and the plate active region 105 b. As a result, the field effect transistor in the second region b may have characteristics suitable for a planar field effect transistor.

FIGS. 4 to 10 are cross-sectional views illustrating methods for forming a semiconductor device according to various embodiments of the present invention taken along line II-II′ and III-III′ of FIG. 3.

Referring to FIG. 4, a substrate 100 includes first and second regions a and b. A mask layer is formed on an entire surface of the substrate 100. The mask layer is patterned to form a first mask pattern 102 a on the substrate 100 of the first region a and to form a second mask pattern 102 b on the substrate 100 of the second region b. The first and second mask patterns 102 a and 102 b may be simultaneously formed. The first and second mask patterns 102 a and 102 b may be formed of photoresist. Alternatively, the first and second mask patterns 102 a and 102 b may be formed of a hard disk layer, such as silicon nitride.

Referring to FIG. 5, the substrate 100 is then etched using the first and second mask patterns 102 a and 102 b as etch masks to form a fin active region 105 a in the first region a and a planar active region 105 b in the second region b. The fin and planar active regions 105 a and 105 b vertically protrude from the substrate 100. The fin active region 105 a is fin-shaped. The top surface of the planar active region 105 b is wider than that of the fin active region 105 a. The etched region of the substrate may be used as a device isolation region.

Referring to FIG. 6, the first and second mask patterns 102 a and 102 b are removed from the fin and planar active regions 105 a and 105 b on the substrate 100. A buffer oxide layer 107 is then formed on a majority of the surface of the substrate 100. Lattice defects in the substrate 100 caused by the etching process may be cured during formation of the buffer oxide layer 107. The buffer oxide layer 107 may be formed by thermal oxidation or chemical vapor deposition (CVD). If the buffer oxide layer 107 is formed by CVD, the oxide layer may be deposited early in the deposition process, such that the lattice defects in the substrate 100 may be cured.

In order to reduce the aspect ratio of the etched region of the substrate 100, an supplemental insulation layer 109 partially fills the etched region of the substrate 100. The supplemental insulation layer 109 may be formed of a Spin-On-Glass (SOG) layer having excellent gap-fill characteristics. The SOG layer may be formed as follows. The SOG layer may be applied to a majority of the surface of the substrate 100 by a spin-coating method. As such, the SOG layer may fill a portion of the etched region despite its high aspect ratio. The SOG layer may then be hardened via a bake process to form the supplemental insulation layer 109. After hardening the SOG layer, an upper portion of the hardened SOG layer may be further recessed to a desired height. The SOG layer may be formed of an HSQ (Hydrogen Silses Quioxane) layer or a polysilazane material such as a TOSZ. In some embodiments, the supplemental insulation layer 109 may be omitted.

Still referring to FIG. 6, a liner layer 111 is formed on a majority of the surface of the substrate 100 including the supplemental insulation layer 109. An insulation layer 113 is formed on the liner layer 111, filling the etched region of the substrate 100. The insulation layer 113 may be formed of silicon oxide. The liner layer 111 may preferably be formed of an insulation layer having an etch selectivity with respect to the insulation layer 113. For example, the liner layer 111 may be formed of silicon nitride.

Referring to FIG. 7, the insulation layer 113, the liner layer 111 and the buffer oxide layer 107 are successively planarized until the top surfaces of the fin and planar active regions 105 a and 105 b are exposed. As a result, a preliminary first liner 111 a and a first device isolation layer 113 a are formed along sidewalls of the fin active region 105 a. A second liner 111 b and a second device isolation layer 113 b are also formed along sidewalls of the planar active region 105 b.

A method for planarizing the insulation layer 113, the liner layer 111 and the buffer oxide layer 107 will now be described. It may be preferable for the insulation layer 113 to be planarized using chemical-mechanical polishing (CMP) until the liner layer 111 is exposed. The insulation layer 113 may also be planarized using isotropic etching. The planarized insulation layer 113 may then be recessed to form the first and second device isolation layers 113 a and 113 b. The exposed liner layer 111 may be etched-back until the buffer oxide layer 107 is exposed to form the preliminary first liner 111 a and the second liner 111 b. The exposed buffer oxide layer 107 may then be removed to expose the top surfaces of the fin and planar active regions 105 a and 105 b.

The liner layer 111 may be etched-back after recessing the planarized insulation layer 113. Alternatively, the planarized insulation layer 113 may be recessed after etching-back the liner layer 111, and the exposed buffer oxide layer 107 may be removed after recessing the planarized insulation layer 113.

To control the threshold voltage of the fin field effect transistor, impurity ions may be implanted into the fin active region 105 a using a first sacrificial oxide layer (not shown). Likewise, to control the threshold voltage of the planar field effect transistor, impurity ions may be implanted into the planar active region 105 b using a second sacrificial oxide layer (not shown). The first and second sacrificial oxide layers may be removed after implanting the respective impurity ions.

Still referring to FIG. 7, an oxidation barrier layer 117 is formed on a majority of the surface of the substrate 100, including the exposed top surfaces of the fin and planar active regions 105 a and 105 b. The oxidation barrier layer 117 may prevent lower layers from being oxidized. In addition, it may be preferable for the oxidation barrier layer 117 to be formed of a material having an etch selectivity with respect to the first and second device isolation layers 113 a and 113 b.

Referring to FIG. 8, the oxidation barrier layer 117 is patterned to expose at least the upper surface of the fin active region 105 a. The patterned oxidation barrier layer 117 a remains on the upper surface of the planar active region 105 b. Also, the patterned oxidation barrier layer 117 a may preferably cover the second liner 111 b.

A capping insulation layer 120 is then formed on an exposed upper surface of the fin active region 105 a using a thermal oxidation process. As a result, the capping insulation layer 120 is selectively formed on the upper surface of the fin active region 105 a. The capping insulation layer 120 is formed to a thickness sufficient to preclude the formation of an inversion-layer channel at the upper surface of the fin active region 105 a.

The capping insulation layer 120 may be formed after the impurity ions are implanted using the above-mentioned sacrificial layers. As such, the capping layer 120 may not be subjected to etching damage when the sacrificial layers are removed.

Referring to FIG. 9, the patterned oxidation barrier layer 117 a is removed from the substrate 100. The preliminary first liner 111 a is selectively recessed to form a first liner 111 a′ on a lower portion of sidewalls of the fin active region 105 a, exposing the buffer oxide layer 107 on the upper sidewalls of the fin active region 105 a. The exposed buffer oxide layer 107 is then recessed to expose the upper sidewall of the fin active region 105 a.

In some embodiments, the oxidation barrier layer 117 may be formed of a material having the same etching rate as the preliminary first liner 111 a. Accordingly, the patterned oxidation barrier layer 117 a and the preliminary first liner 111 a may be simultaneously removed by adjusting the thickness of the oxidation barrier layer 117. Also, a wet etching process may be used. The oxidation barrier layer 117 may be formed of silicon nitride.

Referring to FIG. 10, first and second gate insulation layers 122 a and 122 b, first and second gate electrodes 125 and 127, and first and second source/drain regions 128 a and 128 b are formed. Methods for forming these elements will now be described.

A first gate insulation layer 122 a on the exposed upper sidewalls of the fin active region 105 a and a second gate insulation layer 122 b on the exposed upper surface of the planar active region 105 b are formed using a thermal oxidation process. Alternatively, the first and second gate insulation layers 122 a and 122 b may be formed by CVD. The first and second gate insulation layers 122 a and 122 b may be formed of the same materials. The first and second gate insulation layers 122 a and 122 b may also be formed to the same thickness. However, the thickness of the capping layer 120 is greater than that of the first and second gate insulation layers 122 a and 122 b.

A gate conductive layer is then formed on the surface of the substrate 100 including the first and second gate insulation layers 122 a and 122 b. The gate conductive layer is patterned to form first and second gate electrodes 125 and 127. The first and second gate electrodes 125 and 127 may be formed of doped polysilicon, polycide, or other conductive material. Other such conductive materials may include metals (such as tungsten or molybdenum), conductive metal nitrides (such as titanium nitride, tantalum nitride or tungsten nitride), or metal silicides (such as tungsten silicide or titanium silicide).

Impurity ions are selectively implanted using the first gate electrode 125 as a mask to form first source/drain regions 128 a in the fin active region 105 a at both sides of the first gate electrode 125. Impurity ions are also selectively implanted using the second gate electrode 127 as a mask to form second source/drain regions 128 b on the plate active region 105 b at both sides of the second gate electrode 127. The first and second source/drain regions 128 a and 128 b may be sequentially formed. Alternatively, the first and second source/drain regions 128 a and 128 b may be formed simultaneously.

As previously mentioned, a capping gate insulation layer is selectively formed only on the upper surface of the fin active region of a substrate having a fin active region and a planar active region. The capping gate insulation layer may be formed to a greater thickness than a first gate insulation layer formed on upper sidewalls of the fin active region and a second gate insulation layer formed on an upper surface of the planar active region, such that an inversion-layer channel is not formed at the upper surface of the fin active region. Alternatively, the capping gate insulation layer may be formed of a material with a higher dielectric strength than the first gate insulation layer to preclude formation of an inversion-layer channel at the upper surface of the fin active region. As such, a fin field effect transistor may have vertical channels along both upper sidewalls of the fin active region, but not at the upper surface of the fin active region, when the transistor is disposed in a forward on-state mode of operation. As a result, it may be possible to minimize the “hump” phenomenon in fin field effect transistors. In addition, the second gate insulation layer may be formed to have suitable characteristics for a planar field effect transistor. Thus, characteristics for both the fin field effect transistor and the planar field effect transistor may be improved.

Many alterations and modifications may be made by those having ordinary skill in the art, given the benefit of present disclosure, without departing from the spirit and scope of the invention. Therefore, it must be understood that the illustrated embodiments have been set forth only for the purposes of example, and that it should not be taken as limiting the invention as defined by the following claims. The following claims are, therefore, to be read to include not only the combination of elements which are literally set forth but all equivalent elements for performing substantially the same function in substantially the same way to obtain substantially the same result. The claims are thus to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, and also what incorporates the essential idea of the invention. 

1. A semiconductor device comprising: a substrate having a first region and a second region; a fin active region protruding from the substrate of the first region; a planar active region protruding from the substrate of the second region; a capping insulation layer disposed on a top surface of the fin active region; a first liner and a first device isolation layer sequentially stacked on a sidewall of the fin active region, the first liner disposed on a portion of the sidewall to expose a upper portion of the sidewall, the first device isolation layer having a top surface higher than that of the first liner; a second liner and a second device isolation layer sequentially stacked on a sidewall of the planar active region; a first gate electrode crossing over the fin active region and the capping insulation layer; a second gate electrode crossing over the planar active region; a first gate insulation layer interposed between the first gate electrode and the exposed portion of the fin active region; and a second gate insulation layer interposed between the second gate electrode and the planar active region, wherein the capping insulation layer has a thickness thicker than a thickness of the first and second gate insulation layers.
 2. A semiconductor device according to claim 1, wherein the capping insulation layer is formed of a thermal oxide.
 3. A semiconductor device according to claim 1, wherein a lower end of the first liner is extended along a surface of the substrate neighboring the fin active region to be in contact with a bottom surface of the first device isolation layer, and wherein a lower end of the second liner is extended along a surface of the substrate neighboring the planar active region to be in contact with a bottom surface of the second device isolation layer.
 4. A semiconductor device according to claim 3, further comprising: a supplemental insulation layer interposed between the first liner and the substrate and between the second liner and the substrate.
 5. A semiconductor device according to claim 1, further comprising: a buffer oxide layer interposed between the fin active region and the first liner and between the planar active region and the second liner.
 6. A semiconductor device according to claim 1, further comprising: first source/drain regions formed in the fin active region on both sides of the first gate electrode; and second source/drain regions formed in the planar active region on both sides of the second gate electrode.
 7. A field effect transistor, comprising: a vertical fin-shaped semiconductor active region having an upper surface and a pair of opposing sidewalls on a substrate; and an insulated gate electrode on the upper surface and opposing sidewalls of the fin-shaped active region, the insulated gate electrode comprising a capping gate insulation layer having a thickness sufficient to preclude formation of an inversion-layer channel along the upper surface of the fin-shaped active region when the transistor is disposed in a forward on-state mode of operation.
 8. The transistor of claim 7, wherein the insulated gate electrode further comprises: a sidewall gate insulation layer on upper sidewalls of the fin-shaped active region, wherein the thickness of the capping gate insulation layer is greater than a thickness of the sidewall gate insulation layer.
 9. The transistor of claim 7, wherein the insulated gate electrode further comprises: a sidewall gate insulation layer on upper sidewalls of the fin-shaped active region, wherein the capping gate insulation layer and the sidewall gate insulation layer comprise different electrically insulating materials and wherein a dielectric strength of the capping gate insulation layer is greater than a dielectric strength of the sidewall gate insulation layer.
 10. The transistor of claim 8, further comprising: a buffer oxide layer on lower sidewalls of the fin-shaped active region; a liner layer on the buffer oxide layer and extending on sidewalls of the fin-shaped active region away from the substrate; and an insulation layer on the liner layer and separated from the fin-shaped active region by the liner layer.
 11. The transistor of claim 10, further comprising: a supplemental insulation layer on the substrate adjacent lower sidewalls of the fin-shaped active region.
 12. The transistor of claim 7, further comprising a planar active region adjacent the fin-shaped active region on the substrate. 